Absorbing nonwoven materials are often used for wiping spills and leakages of all kinds in industrial, service, office and home locations. The basic synthetic plastic components normally are hydrophobic and will absorb oil, fat and grease, and also to some degree water by capillary force. To reach a higher water absorption level, cellulosic pulp is often added. There are many demands put on nonwoven materials made for wiping purposes. An ideal wiper should be strong, absorbent, abrasion resistant and exhibit low linting. To replace textile wipers, which is still a major part of the market, they should further be soft and have a textile touch.
Nonwoven materials comprising mixtures of cellulosic pulp and synthetic fibres can be produced by conventional papermaking processes, see e.g. U.S. Pat. No. 4,822,452, which describes a fibrous web formed by wetlaying, the web comprising staple length natural or synthetic fibres and wood cellulose paper-making fibres wherein an associative thickener is added in the furnish.
Hydroentangling or spunlacing is a technique introduced during the 1970's, see e.g. CA patent no. 841 938. The method involves forming a fibre web which is either drylaid or wetlaid, after which the fibres are entangled by means of very fine water jets under high pressure. Several rows of water jets are directed against the fibre web which is supported by a movable fabric. The entangled fibre web is then dried. The fibres that are used in the material can be synthetic or regenerated staple fibres, e.g. polyester, polyamide, polypropylene, rayon or the like, pulp fibres or mixtures of pulp fibres and staple fibres. Spunlace materials can be produced in high quality to a reasonable cost and have a high absorption capacity. They can e.g. be used as wiping material for household or industrial use, as disposable materials in medical care and for hygiene purposes etc.
In WO 96/02701 there is disclosed hydroentangling of a foamformed fibrous web. Foamforming is a special variant of wetlaying where the water besides fibres and chemicals also contains a surfactant which makes it possible to create a foam where the fibres can be enmeshed in and between the foam bubbles. The fibres included in the fibrous web can be pulp fibres and other natural fibres and synthetic fibres.
Through e.g. EP-B-0 333 211 and EP-B-0 333 228 it is known to hydroentangle a fibre mixture in which one of the fibre components consists of meltblown fibres which is one type of spunlaid filaments. The base material, i.e. the fibrous material which is exerted to hydroentangling, either consists of at least two combined preformed fibrous layers where at least one of the layers is composed of meltblown fibres, or of a “coform material” where an essentially homogeneous mixture of meltblown fibres and other fibres is airlaid on a forming fabric.
Through EP-A-0 308 320 it is known to bring together a prebonded web of continuous filaments with a separately prebonded wetlaid fibrous material containing pulp fibres and staple fibres and hydroentangle together the separately formed fibrous webs to a laminate. In such a material the fibres of the different fibrous webs will not be integrated with each other since the fibres already prior to the hydroentangling are bonded to each other and only have a very limited mobility. The material will show a marked twosidedness. The staple fibres used have a preferred length of 12 to 19 mm, but could be in the range from 9.5 mm to 51 mm.
One problem is clearly seen in hydroentangled materials—they will very often be markedly twosided, i.e. it can clearly be discerned a difference between the side facing the fabric and the side facing the water jets in the entangling step. In some cases this has been used as a favourable pattern, but in most cases it is seen as a disadvantage. When two separate layers are combined and fed into an entangling process, normally this process step cannot thoroughly mix the layers, but they will still exist, albeit bonded to each other. With pulp in the composite there will be a pulp-rich side and a pulp-poor side, which will result in differing properties of the two sides. This is pronounced when spunlaid filaments are used as they tend to form a flat two-dimensional layer when created, which will mix poorly. Some producers have tried to first add a covering layer and entangle from one side and then turn the web around and add another covering layer and entangle from the other side, but most of the fibre-moving occurs very early in the entangling process, and this more complicated way does not fully solve the problem.
Another problem when using a filament web in a hydroentangled material is that there will be fewer free fibre ends, as the filaments in principle are without ends, and only staple and pulp fibres can contribute to this. Especially polymer fibre ends are what will give the material a textile feeling by their softening effect. The pulp fibres often used in composites will have many free ends but as they engage in hydrogen bonds they will not contribute to a soft textile feeling; instead they will make the resulting material feel much harsher. Thus to get a soft textile material it is important to have a high percentage of textile, i.e. synthetic, staple fibres.